For brevity, a semiconductor manufacturing process is called a process. Due to uncontrollable manufacturing variations, a process can result in typical transistors, fast transistors, or slow transistors. Compared with a typical transistor, a fast transistor has a higher driving capability and provides a larger current. In contrast, a slow transistor has a lower driving capability and provides a smaller current than a typical transistor. A fast transistor is also called a strong transistor while a slow transistor is also called a weak transistor.
An N-type metal-oxide semiconductor transistor is called an NMOS transistor, and a P-type MOS transistor is called a PMOS transistor. A process that results in a typical NMOS and a typical PMOS transistor is called a typical typical (TT) process or a TT process corner. A process that results in a slow NMOS transistor and a fast PMOS transistor is called a slow fast (SF) process corner. A process that results in a fast NMOS transistor and a slow PMOS transistor is called a fast slow (FS) process corner. Transistors behave differently in different process corners.
In a dynamic random access memory (DRAM) circuit, a pair of bit lines serves as both data input and output for the DRAM cell. A voltage, such as a voltage VBL, is used to pre-charge the bit lines. Pre-charge refers to charging the bit lines before a write or a read operation. Further, voltage VBL is generated based on a reference voltage, such as a voltage VREF. In various situations, a value of voltage VBL is the same as that of voltage VREF, and is a fixed value for different process corners.
In an existing approach, a value of voltage VREF and of voltage VBL is a percentage of a supply voltage VDD, such as 50% of supply voltage VDD. In another approach, a value of voltage VREF and of voltage VBL is generated based on a supply voltage VDD and has a constant value, such as 0.5 V, for example. In both situations, because of manufacturing process variations, the fixed value of voltage VBL in different process corners degrades performance of a sense amplifier used in conjunction with voltage VBL. Further, there is no mechanism to adjust voltage VREF and voltage VBL to compensate for the manufacturing process variations.
Like reference symbols in the various drawings indicate like elements.